1. Field of the Invention
The invention relates to a semiconductor laser device and a manufacturing method thereof, and in particular, relates to a semiconductor laser device including multiple integrated semiconductor laser elements and a manufacturing method thereof.
2. Description of Related Art
Compact disk (CD)/compact disk-recordable (CD-R) drives include semiconductor laser elements emitting infrared light with a wavelength of about 780 nm (infrared semiconductor laser elements) as light sources. Digital versatile disk (DVD) drives include semiconductor laser elements emitting light with a wavelength of about 650 nm as light sources.
On the other hand, DVDs which are recordable and capable of playback using blue-violet light with a wavelength of about 405 nm have been developed in recent years. For recording and playback of such DVDs, next-generation DVD drives including semiconductor laser elements emitting light with a wavelength of 405 nm have also been developed simultaneously. Those DVD drives need to be compatible with conventional CDs, CD-Rs and DVDs.
The compatibility with conventional CDS, DVDS, and DVDs recordable and capable of playback in this case is achieved, for example, by a method of providing a DVD drive with plural optical disk pick-up devices emitting infrared, red, and blue-violet light beams, respectively, or by a method of providing an optical disk pick-up device with infrared, red, and blue-violet semiconductor laser devices individually. However, these methods lead to an increase in the number of parts, thus making it difficult to miniaturize optical disk pick-up devices, simplify the structure thereof, and lower the prices.
To prevent such an increase in the number of parts, an infrared semiconductor laser element (wavelength: about 780 nm) and a red semiconductor laser element are formed together on a GaAs substrate to be integrated into a single chip as a semiconductor laser element, which is already put into practical use. Moreover, by integrating semiconductor laser elements into a single chip, light emitting positions of the semiconductor laser elements for respective wavelengths are formed accurately.
In contrast, blue-violet semiconductor laser elements are not formed on GaAs substrates. It is therefore very difficult to integrate a blue-violet semiconductor laser element with the infrared and red semiconductor laser elements into a single chip. Moreover, in order to reduce losses and aberrations of laser light beams emitted from the semiconductor laser elements for respective wavelengths, the light emitting positions thereof need to be located as close as possible to each other.
To this end, there have been proposed integrated semiconductor laser devices which have a structure obtained by forming individual semiconductor laser elements on different substrates and then bonding the substrates to each other so that light emitting layer sides of the semiconductor laser elements (semiconductor element layers) can face each other.
Japanese Patent Application Publication No. 2006-269987 publication (Patent Literature 1) discloses an integrated semiconductor laser device of a single chip obtained by bonding a blue-violet semiconductor laser element to a monolithic semiconductor laser element including red and infrared semiconductor laser elements so that the light emitting layers thereof (on the p-side semiconductor layer side) face each other. In the semiconductor laser device described in Patent Literature 1, p-side pad electrodes of the blue-violet, red and infrared semiconductor laser elements are separately formed on a joint surface between the blue-violet and monolithic semiconductor laser elements. In a plan view thereof, each of the p-side pad electrodes extends in the resonator direction of the laser element and a part of each electrode has a protrusion extending in a direction substantially perpendicular to the resonator direction. The protrusions of the three p-side pad electrodes extend in the same direction at predetermined intervals and are wire-bonded at an end of the semiconductor laser device in the element width direction.
Japanese Patent Application Publication No. 2008-124218 (Patent Literature 2) discloses an integrated semiconductor light emitting element including: a first light emitting element in which an AlGaInP semiconductor laser element and a GaAs semiconductor laser element are formed and integrated in a single chip on a substrate; and a second light emitting element made of a nitride semiconductor laser element. The first and second light emitting elements are arranged on a support base and are bonded to each other so that the light emitting layers thereof (on the p-side semiconductor layer side) can face each other. In the semiconductor laser device described in Patent Literature 2, p-side pad electrodes of the respective semiconductor laser elements are separately formed on a joint surface between the first and second light emitting elements. In a plan view thereof, each of the p-side pad electrodes extends in the resonator direction of the laser element and a part of each electrode has a protrusion (a wire bonding portion) extending in a direction substantially perpendicular to the resonator direction. The protrusions of the three p-side pad electrodes are configured to pass through predetermined regions and finally be wire-bonded at an end of the semiconductor laser device in the element width direction.
However, in the semiconductor laser device disclosed in Patent Literature 1, it is necessary to provide extra areas for wire bonding (the end portions of the protrusions) of the three p-side pad electrodes at the end of the semiconductor laser device in the element width direction. For this reason, the width of the semiconductor laser device is increased by the exclusive wire bonding areas. Therefore, there is a problem that it is difficult to reduce the width of the semiconductor laser device.
Also in the semiconductor light emitting element disclosed in Patent Literature 2, it is necessary to provide the areas for wire bonding (the end portions of the protrusions) of the three p-side pad electrodes at the end of the integrated semiconductor light emitting element in the width direction. For this reason, the width of the semiconductor laser device is increased by the amount of the exclusive wire bonding areas. Therefore, there is a problem that it is difficult to reduce the width of the semiconductor light emitting element.